The objective of this project will be to study the immediate and long term beneficial or detrimental effects of laser radiation on the atheroslcerotic plaque and normal arteries in various animal models. Work done by the principal investigator has demonstrated the feasibility of using lasers adapted to a fiberoptic-catheter delivery system to re-establish new vascular channels in totally occluded human necropsy coronary arteries. This was accomplished under a blood or saline media. Also, preliminary work in the living rabbit atherosclerotic model continues to demonstrate the ability of the laser delivered through a fiberoptic system to recannalize arteries obstructed by atherosclerosis. The laser injury to plaque is a clean incision which on cross section of the artery shows the plaque divided into wedge-shaped segments. Angiography did not reveal any debris in the distal vessels following laser radiation of the rabbit atherosclerotic model. To further test whether distal embolization will occur following laser radiation a dog model using transplanted human atherosclerotic coronary arteries will be evaluated. Filters will be placed distally to the lased site to collect debris. In other dogs (with normal arteries) long term studies will be done to evaluate the potential detrimental effects of laser radiation on the vessel wall, i.e., aneurysm, perforation, thrombosis, over a one month period of time. The vessels will be studied by light and electron microscopic techniques. Additional experiments will be done to study the long term effects of laser radiation on vessels of atherosclerotic monkeys. These vessels will be evaluated by light and electron microscopy. In all of these experiments, the amount of laser energy (watts X time) used will be recorded in rder to determine optimal ranges to recannalize obstructed vessels without producing significant vessel wall damage.